This invention relates to brush seals. Specifically, this invention relates to bristle arrangements for brush seals.
Gas turbine engines commonly use brush seals. The brush seals typically prevent secondary flow from escaping through a gap between a stationary part (e.g. a diffuser case) and a rotating part (e.g. a turbine shaft). The brush seal can have other uses, such as sealing a gap between stationary parts.
Several sub-assemblies form a brush seal. The sub-assemblies typically include packs of wire bristles and various plates. A one stage brush seal has a side plate and a back plate that sandwich the bristles therebetween. To increase capability, the engine could use a multiple stage brush seal. The multiple stages allow a greater pressure drop across the brush seal from the upstream side to the downstream side.
The design process and the assembly of conventional brush seals have several drawbacks. First, the sub-assemblies of a conventional brush seal are specific to a particular brush seal size. In other words, one cannot use the sub-assemblies from a larger brush seal to build a smaller brush seal. Nor could one use the sub-assemblies from a smaller brush seal to build a larger brush seal. The inability to use a sub-assembly in more than one brush seal size has an impact on inventory and space requirements. Assembling brush seals of different sizes requires keeping every sub-assembly in inventory. All of these sub-assemblies take up space.
Second, the fixtures used to make the conventional sub-assemblies are also specific to each sub-assembly size. One cannot use the fixture designed for a smaller sub-assembly to make a larger sub-assembly. Nor could one use the fixture designed for a larger sub-assembly to make a smaller sub-assembly. The inability to use a fixture for making more than one sub-assembly size also impacts inventory and space requirements. Assembling different size sub-assemblies requires keeping every fixture in inventory. All of these fixtures take up even more space.
Third, developing a new brush seal is time consuming. As described above, the operator cannot use a current sub-assembly to make a new size of brush seal. A designer would have to design all new sub-assemblies for the new size brush seal.
Fourth, developing a new brush seal can be costly. As described above, one cannot use the existing fixtures to make new size sub-assemblies. The designer, in addition to designing the brush seal sub-assemblies, would also have to design fixtures for each new part.
Fifth, current assembly techniques do not allow for the rework of certain sections of the brush seal. If the brush seal has unsuitable characteristics (e.g. the bristle pack), then the entire brush seal is usually scrapped.